July 31, 19 13] 



NATURE 



573 



other parts of the body. The larval form lives in the 

 body of some invertebrate — in a few known cases in 

 a mosquito, or in a crustacean. The microfilarias 

 were discovered by Demarquay in 1863. Many of 

 them show a remarkable periodicity, some appearing 

 in the blood at an exact hour at night, and some in 

 the day, for which phenomenon there is at present 

 no satisfactory explanation. 



Some are short, and some long, and some are en- 

 capsuled, others not. Filarial cause various diseases, 

 probably elephantiasis, and certainly enormous vari- 

 cosities of the lymphatics, chyluria, chylous dropsy, 

 Calabar swelling, and certain tumours. 



We now come to the trvpanosomes. They are 

 flagellated organisms, which are the cause of many 

 deadly diseases in men and animals, such as sleeping 

 sickness, nagana (or tsetse-fly disease), surra, mal- 

 de-caderas, dourine, and others. They are transferred 

 from animal to animal by biting flies, fleas, lice, and 

 leeches, in which the sexual part of their life-cycle 

 takes place. The first one was seen in the blood of 

 a frog by Gluge in 1842. 



A type example is T. lewisi in the blood of a rat. 

 This was discovered by Lewis in 1878, and is found 

 in about 25-29 per cent, of wild rats. Some die, but 

 most recover and become immune ; it is a very specific 

 parasite, and cannot be transferred to any other kind 

 of animal. 



The T. brucei, causing nagana or tsetse-fly disease, 

 probably exists in the wild game of South Africa, 

 much as the T. lewisi does in the wild rats, but when 

 it is carried by the tsetse-fly to domesticated animals 

 it kills them one and all in enormous numbers. 



The T. gambiense, which causes sleeping sickness, 

 was first seen by Dutton in 1902, and is carried by 

 another species of tsetse-fly. 



Nature attempts to fight against these invaders by 

 phagocytosis. The parasites, however, multiply so 

 rapidly that this method of attack is not very effectual ; 

 it can only be so in very early infections, and probably 

 it then often is, that is, before the parasite has had 

 time to start dividing. At the present time the question 

 of trypanosomosis amongst man and animals is, for 

 many countries which have colonies, of the greatest 

 economic importance, so that a great deal of work 

 has been done in the attempt to find a cure. A great 

 manv drugs, new and old, have been tried, and some 

 good has been done. The first drug which was found 

 to be of service was arsenic, first in simple and then 

 in complex combination, and the subcommittee of the 

 Royal Society, formed for the purpose of supervising 

 experiments in this direction, suggested the trial of 

 antimony in these diseases, on account of its near 

 chemical relationship to arsenic. 



This has given better results than arsenic, and a 

 commission is at present at work in Africa, in the 

 Lado district, trying its effects on a large scale. We 

 found that the salts of antimony were too rapidly 

 eliminated from the body to be successful in the larger 

 animals and man, and so we devised a very finelv 

 divided form of the metal itself which we put directly 

 into the circulation, and this has given, so far, the 

 best results. The leucocvtes eat it up and transform 

 it slowly into some soluble form, taking, in a horse, 

 for instance, four days to dispose of one dose, and 

 the effect of this is much more profound and lasting 

 tfian that of the salts. But some trvpanosomes 

 always escape, since one dose is never sufficient for 

 cure. In rats with nagana. in which the trvpano- 

 somes bv the fifth and sixth day may number 3,000,000 

 per cubic millimetre of blood, the minimum number 

 of doses for cure has been found to be four, and with 

 this dosage it is possible to cure 100 per cent, of rats. 

 So there is still some hope. 



It is interesting in this connection to remember 

 NO. 2283, VOL. 91] 



what Bacon, whose death, you know, was due to an 

 experiment he undertook to prove . the preservative 

 action of intense cold upon animal bodies, says, 

 " Laying aside therefore all fantastic notions con- 

 cerning them, I fully believe, that if something could 

 be infused in very small portions into the whole sub- 

 stance of blood ... it would stop not only all putre- 

 faction, but arefaction likewise, and be very effectual 

 in prolonging life." His vision was prophetic ! 



The bird trypanosomes are very much larger than 

 the mammalian variety, are very dense, and move 

 much more slowly. 



An example of an organism very closely allied to 

 the trvpanosomes which is found only in fishes' blood 

 is the trypanoplasma. It has two flagella, and the 

 micronucleus is very large. This organism is prob- 

 ably transferred by leeches, but very little is yet known 

 of it. 



There are other flagellated organisms which may 

 appear in the blood and live there as accidental para- 

 sites. There is a kind of inflammation of the intes- 

 tines in reptiles (in the large sense) which causes 

 the mucosa of the intestine to become permeable, so 

 that some of the organisms which live in the intestine 

 are able to get into the blood and live there. The 

 onlv mention of these organisms in the blood is by 

 Danilewsky, who in 1889 found hexamitus in the 

 blood of a frog and tortoise. When in the blood they 

 appear to excite a general oedema and ascites. I have 

 found them now in nine cases. These are interesting 

 as showing the power of adaptation to new surround- 

 ings possessed by these parasites. 



I now come to the intracellular parasites. 



Schaudinn thought that the bird trypanosomes had 

 an intracellular stage, and if this were so they would 

 form a bridge between the extra-cellular parasites, of 

 which I have shown you types, and the intracellular 

 parasites we are about to consider. But Schaudinn 

 seemed, with his verv brilliant attainments, to want a 

 little more ballast of medical earth-knowledge. His 

 work on this point has not been confirmed, and he 

 was probably misled by a double, or even treble in- 

 fection, so that we must think of these intracellular 

 parasites as quite distinct from the others. 



I will take first the Plasmodium praecox, the cause 

 of the malaria in birds, as this parasite is of great 

 historical interest; for it was Ross's work on this 

 organism and his discovery of the rest of its life- 

 cvcle in the mosquito, which enabled him — on account 

 of the great likeness between this and the parasite 

 causing' human malaria — to deduce from the one the 

 etiology of the other, which was confirmed by Grassi and 

 others. The Plasmodium praecox is, in many stages, 

 so like human malaria that it can only be differentiated 

 bv the presence of the oval nucleus of the bird's red 

 corpuscles. The life-cycle is very complex, part taking 

 place in the blood of the bird, and another part 

 (sexual reproduction) in the body of a mosquito. This 

 parasite was first seen by Grassi in 1890; it is very 

 widely distributed, and is very deadly to birds. 



Human malaria has been known for centuries. 

 Varro, who knew a good deal about what we should 

 now call hvsriene, more than a century B.C., thought 

 that malarial fevers were due to invisible animals, 

 which entered the bodv with the air in breathing - , 

 and Vitruvius, Columelhis, and Paladius were of the 

 same opinion. Now we know that the mosquito is 

 aeain the carrier, and that the sexual part of the 

 parasite's cvcle takes place in it, but whether the 

 mosquito alone can account for all the phenomena of 

 malaria is not vet quite certain. 



There are three varieties of malaria in man — the 

 tertian, auartan. and quotidian : in the tertian the 

 cycle of the parasite in the bodv takes fortv-eight hours, 

 and in quartan seventv-two hours, and in pernicious 



